The use of a light emitting diode (LED) is an effective means of producing light. Relatively small LEDs (i.e., having a diameter less than 100 microns) have the benefit of more efficient cooling than larger LEDs. Part of the efficiency is attributed to the LED s being capable of being spaced further apart and yet still yield effective light output on a per unit area basis.
The use of Stokes shifting phosphors is a known means of taking a relatively narrow wavelength of emitted light from LEDs (e.g. 470 nm) and converting a portion of that light into a broader range of longer wavelengths, thus creating “white light” that is desired in many lighting applications. One disadvantage of using down shifting phosphors is the accompanying energy (and thus efficiency) loss in the process. Much of the energy lost in larger LEDs is a result of light being re-emitted from the phosphor back into the LED from which the original light originated. This re-captured light is eventually lost and converted into heat, and in a system where the phosphor is coated directly onto the surface of the LED (most available “white light” LEDs), this can result in >50% loss in efficiency. There is a need, then, to maximize the light output from an LED, particularly when phosphors are used, specifically when micro LEDs are used.
The use of using reflective materials around a mesa containing a LED in a light emitting laminate is reported. However these laminates typically apply LEDs via a pick and place or transfer printing technique. These manufacturing techniques lend themselves to more elaborate or complicated designs (such as mesas) but are not a cost effective from a large scale manufacturing perspective. There is a need for a laminate that is cost effective to make and that minimizes efficiency attributable to TIR, particularly when micro LEDs are employed.
WO 2011/082497 Al; EP 2 325 903 A1; US 2011/0204020 A1; U.S. Pat. No. 7,799,699